directional shadow mapping in lovr

directional_shadow.lua

local light_pose = lovr.math.newMat4()
local light_view = lovr.math.newMat4()
local light_projection = lovr.math.newMat4():perspective(math.rad(120), 1, 0.01)
--light_projection:orthographic(-5, 5, -5, 5, 100, -100) -- why is near and far inverted? ¯\_(ツ)_/¯

local depthBufferSize = 1024
local depthtex = lovr.graphics.newTexture(depthBufferSize, depthBufferSize, {format = 'd32f', mipmaps = false, usage = {'render', 'sample'}})

local shadowmapper = lovr.graphics.newShader(
[[
layout( push_constant ) uniform constants {
  mat4 LightSpaceMatrix;
} PushConstants;
layout(location = 1) out vec4 PositionLight;

vec4 lovrmain() {
  PositionLight = PushConstants.LightSpaceMatrix * Transform * vec4(VertexPosition.xyz, 1.f);
  return DefaultPosition;
}
]],[[
layout(set = 2, binding = 0) uniform texture2D DepthBuffer;
layout(location = 1) in vec4 PositionLight; // fragment position inside the light-space

vec4 lovrmain() {
  vec2 projCoords = PositionLight.xy / PositionLight.w * 0.5 + 0.5;
  float closestDepth;
  if ((projCoords.x > 0.) && (projCoords.x < 1.) &&
      (projCoords.y > 0.) && (projCoords.y < 1.))
    closestDepth = getPixel(DepthBuffer, projCoords).r;
  else
    closestDepth = 0.;
  float currentDepth = PositionLight.z / PositionLight.w;
  float currentDepth_biased = currentDepth + 0.00003;
  float shadow = (currentDepth_biased < 0. || closestDepth < currentDepth_biased) ? 1.0 : 0.3;
  vec4 color = DefaultColor;
  return color * vec4(vec3(shadow), 1.0);
}
]])


function drawScene(pass, depthFromLight)
  local t = lovr.timer.getTime()
  pass:setColor(0xf2b63d)  -- rotating fan
  pass:box(mat4(0, 1.75, -4):rotate(t, 0,1,0):rotate(math.pi / 3 * 0, 0,1,0):rotate(math.rad(10), 1,0,0):scale(1, 0.05, 0.15))
  pass:box(mat4(0, 1.75, -4):rotate(t, 0,1,0):rotate(math.pi / 3 * 1, 0,1,0):rotate(math.rad(10), 1,0,0):scale(1, 0.05, 0.15))
  pass:box(mat4(0, 1.75, -4):rotate(t, 0,1,0):rotate(math.pi / 3 * 2, 0,1,0):rotate(math.rad(10), 1,0,0):scale(1, 0.05, 0.15))
  pass:setColor(0x8fcccb)   -- a vertical box
  lovr.math.setRandomSeed(1)
  for _ = 1, 20 do  -- some boxy columns
    local height = lovr.math.randomNormal(0.2, 1)
    local shade = 0.3 + 0.4 * lovr.math.random()
    pass:setColor(shade, shade, shade)
    pass:box(
      lovr.math.randomNormal(5, 0),
      height / 2,
      lovr.math.randomNormal(5, -4),
      0.3, height, 0.3)
  end
  pass:setColor(0xd46e33)  -- the floor
  pass:box(0, 0, 0, 50, 0.2, 50)
end


function lovr.update(dt)
  local t = lovr.timer.getTime() / 8
  light_pose:target(
    vec3(1, 2.5, -4):add(2 * math.sin(t), 0, math.cos(t)),
    vec3(0, 0, -4))
  light_view:set(light_pose):invert()
  -- render to depth buffer from light perspective
  local pass = lovr.graphics.getPass('render', {depth = {texture=depthtex}, samples = 1})
  pass:setCullMode('front')
  pass:setProjection(1, light_projection)
  pass:setViewPose(1, light_pose)
  drawScene(pass)
  lovr.graphics.submit(pass)
end


function lovr.draw(pass)
  --[[ debug-output of depth buffer texture
  local w, h = lovr.system.getWindowDimensions()
  local size = h / 4
  pass:setViewport(0, 0, size, size)
  pass:fill(depthtex)
  pass:setViewport(0, 0, w, h)
  --]]
  pass:setCullMode('back')
  pass:setColor(0xfff4e0)
  pass:cone(mat4(light_pose):rotate(math.pi, 0,1,0):scale(0.07)) -- light position

  pass:setShader(shadowmapper)
  local light_space_matrix = light_projection * light_view
  pass:send('LightSpaceMatrix', light_space_matrix)
  pass:send('DepthBuffer', depthtex)
  drawScene(pass)
end